Effective utilization of coal has attracted attention as a last resort to the recent energy issue. To convert coal to a high-value added energy medium, advanced technologies such as a technology for gasifying coal and a technology for purifying the gasified gas are employed.
The gasified coal gas contains carbonyl sulfide (COS) and hydrogen cyanide (HCN), which cause air pollution. Hence, it is important to remove these compounds in a gas purification step.
A purification process of gasified coal gas may be configured, for example, as shown in FIG. 1. Specifically, gas obtained by gasifying coal in a gasification furnace 4 and subjected to a dust removal treatment in a dust removal apparatus 5 is introduced into a COS conversion apparatus 6 to convert COS in the gas to carbon dioxide (CO2) and hydrogen sulfide (H2S), which are then recovered in an H2S/CO2 recovery apparatus 7. The thus purified gas is then used for synthesis 8 of chemicals, electric power generation 9, or the like.
Moreover, systems are also proposed in which the purified gas obtained by gasifying and purifying coal is applied to synthesis of chemicals such as methanol and ammonia or used directly for electric power generation. The electric power generation system includes the integrated coal gasification combined cycle (IGCC) system (for example, Patent Document 1). Specifically, in this system, coal is converted to a combustible gas in a high-temperature and high-pressure gasification furnace, and electric power is generated by a combination of a gas turbine and a steam turbine using the gasified gas as a fuel.
The COS conversion is based on the hydrolysis reaction represented by the following Formula (1), and an example of the catalyst for the hydrolysis is a catalyst obtained by supporting a metal carbonate on titanium dioxide (Patent Document 2).[Math 1]COS+H2O→CO2+H2S  (1)
Meanwhile, HCN can be converted to ammonia (NH3) by the hydrolysis reaction of the following Formula (2) or the reaction of Formula (3), and the ammonia can be recovered. An example of the catalyst for hydrolysis of HCN is a titanium dioxide-based composition containing a combination of titanium dioxide, a sulfate of an alkaline-earth metal, and a doping compound (Patent Document 3).[Math 2]HCN+H2O→NH3+CO  (2)HCN+3H2→NH3+CH4  (3)